A liquid crystal display (LCD) comprises liquid crystal material contained within two spaced-apart liquid crystal substrates which are sealed at the periphery. Conventionally, LCDs are manufactured by assembling the substrates in a spaced-apart relation, sealing the substrates together around their periphery with the exception of one or more fill ports to form an enclosure, inserting the liquid crystal material between the substrates and sealing the fill ports. The liquid crystal material is inserted into the display only after most processing of the other components is completed because many types of liquid crystal material may be decomposed by the temperatures utilized, for example, to heat-seal the periphery.
Sealing of the fill port has been a very troublesome step in the manufacture of LCDs. The problems associated with fill port sealing are partially due to the fact that there are a number of different surfaces to which the sealant must simultaneously form a stable adhesive bond of acceptable strength, partially due to the sensitivity of liquid crystal materials to any impurities that can leach out of the sealant and partially due to their sensitivity to elevated cure temperatures. The adverse effects of any of these problems include failure of the seal, loss of alignment of the liquid crystal material, loss of on/off capability of the display, a significant increase in the voltage required to switch the display, and the like.
The difficulty encountered to date in effectively sealing the fill port of an LCD is apparent when one considers the variety of means and agents that have been proposed as solutions to the problem. For example, U.S. Pat. No. 4,470,668 discloses sealing LCDs made of flexible polymeric film with a solvent-free, reaction-setting polysiloxane polymer; U.S. Pat. No. 4,500,171 discloses a method of welding the fill port closed using heat and pressure; U.S. Pat. No. 4,135,789 discloses sealing the fill port with a glass bead which is separated from the liquid crystal by an inert insulating pad; U.S. Pat. No. 4,494,825 discloses a photosetting sealant composition comprising an acrylic or methacrylic resin and at least two photosensitizers which differ in curing time; U.S. Pat. No. 4,325,610 discloses a sealing composition comprising a polyamide or a linear saturated polyester, an epoxy resin and/or an isocyanate compound and a solvent therefor which also is a solvent for the LCD panel which is formed of polyester or polyether sulfone; and U.S. Pat. No. 4,536,060 discloses a two-layer seal for LCDs, the outer layer comprised of a thermoplastic polyamide and the inner layer composed of a saturated polyester. An improved composition for effectively sealing the fill port of an LCD is provided herein.